Shipment of blood and perishable biological materials is problematic because of the short effective life of these product, and their high value. In general, insulated containers in combination with temperature-control agents, such as refrigerant materials, are widely used as a cost-effective system to maintain the temperature of shipped products at selected temperature ranges, including refrigeration (2-8° C.); room temperature (20-30° C.); or frozen (below 0° C.). The temperature-control agents are generally phase change materials, ice, gel packs, or dry ice.
Phase change materials are materials which may be repeatedly converted between solid and liquid phases and utilize their latent heats of fusion to absorb, store and release energy to heat or cool during such phase conversions. In contrast to a material that absorbs and releases energy essentially uniformly over a broad temperature range, a phase change material absorbs and releases a large quantity in the vicinity of its melting/freezing point, thus facilitating temperature maintenance near the melting/freezing point.
Passive refrigerant systems utilizing insulated containers and phase change materials (and/or ice, gel packs, or dry ice) provide sufficient refrigeration for relatively short shipping periods, where, as an additional condition, the ambient temperature does not vary greatly from the internal temperature for extended periods. As shipment times are often longer than the period where ice in an insulated container will melt completely, refrigerant systems using combinations of phase change materials, gel packs and insulated containers are commonplace for shipment of temperature-sensitive products. See, e.g., U.S. Pat. Nos. 7,849,708 and 7,294,374 and US Publication No. 20120197810 (all of which are incorporated by reference). Other systems of insulated containers and phase change materials can be used to extend the time that products within are maintained at room temperatures or at temperatures below freezing (and the latter systems may also include ice or gel packs or dry ice, as appropriate), so as to match the shipment period and the shipment conditions (most importantly, the ambient temperature). See US Publication No. 20120197810.
One issue which has not been addressed is how to best retain the value of blood and other perishable products during shipment. Units of whole blood and red blood cells are kept refrigerated at (1-6° C.), with maximum permitted storage periods (shelf lives) of 35 and 42 days respectively. Platelets are typically pooled before transfusion and have a shelf life of five days—or three days, assuming it takes two days following collection to complete their testing. Platelets are stored at room temperature (22.2° C.) and must be rocked. If there are significant temperature excursions during shipment of blood and biological products, it renders these products unacceptable for medical uses and thus valueless.
Thus for shipping blood and biological products with passive refrigerant systems, sufficient refrigerant must always be present to maintain the required storage temperature. The ambient temperature significantly affects the conversion rate of the refrigerant, and thus the time blood and biological products can be in shipment before an unacceptable temperature excursion takes place.
Time in shipment can only be estimated, as there are many sources of delay during shipment, both conventional and unexpected. Also, the temperature during shipment can only be estimated based on expected weather conditions and knowledge of shipment mode internal temperatures and warehouse temperatures. If a shipment of blood or biological products is delayed, and/or the temperature varies beyond expectation during shipment, it is important to determine how much time is left before a sufficient quantity of the refrigerant is converted to cause an unacceptable temperature excursion.